This invention relates to a liquid crystal display element, more particularly to a liquid crystal display element having liquid crystal orientation controlling film made from a special polyhydrazimideimide.
Heretofore, as the liquid crystal orientation controlling film used in nematic liquid crystal display elements applying electro-optical effect operated particularly by the action of electric field, there have mainly been used inorganic material films such as silicon monooxide film produced by an oblique vacuum vaporization method or the like. This is because the inorganic films have no factor giving bad influence on liquid crystals used together since they do not dissolve the liquid crystals when contacted and have an advantage in that they can orientate Schiff base type liquid crystals and biphenyl type liquid crystals uniformly. The silicon monooxide oblique vacuum vaporized film is excellent in transparency, but has a defect in that patterns formed by transparent electrodes made of metal oxide film (hereinafter referred to as "partially reflected pattern") are easily observable when such patterns should not be observable.
On the other hand, there have been developed liquid crystal display elements using as the liquid crystal orientation controlling film a film made from organic polymer materials and orientation treated by rubbing in one direction by means of a cloth or the like. But when organic polymer materials are used as the liquid crystal orientation controlling film (or simply "the orientation film") there are many defects in that almost organic polymer materials can hardly produce uniformity in liquid crystal orientation, non-uniformity in the orientation is easily increased by deterioration caused by passing an electric current for a long period of time, and the like.
Among organic polymer materials, some polyimides are known as forming orientation films having relatively excellent orientation properties. For example, U.S. Pat. No. 3,994,567 discloses polyimides such as produced by reacting 4,4'-diaminodiphenyl ether with pyromellitic dianhydride, said polyimides being considerably good in uniformity in orientation and in durability by a weathering test. But there are many problems in using such polyimide films, since browning of such polyimides remarkably proceeds by heating at the time of removal of the solvent and ring closure by dehydration, which results in producing browning in a liquid crystal display element after placing a liquid crystal material therein, making the visual field dark at the same time, also lowering contrast and not satisfying the requirements for performance as display element, particularly for display of high quality. On the other hand, when polyimide-isoindoloquinazolinedione is used as the polyimide according to U.S. patent application Ser. No. 1161, filed Jan. 5, 1979, now abandoned, the sealing by using frit glass at 450.degree. C. becomes possible and the reliability (poor in blotting) is improved but the orientation film is undesirably colored.
Recent increasing demand for liquid crystal cells having a multilayer structure wherein two or more liquid crystal layers are laminated by interposing transparent substrates requires polyimide orientation films which do not show such coloring as mentioned above.